1. Field of the Invention
The present invention generally relates to cell membrane permeability monitoring, and in particular to a device and method for detecting changes in cell membrane permeability.
2. Description of the Prior Art
Before an ischemic and potentially fatal or at least dangerous event occurs in a tissue, it is often preceded by anoxic conditions in cells. If the cells get too little oxygen, the cell metabolism fails and the transport in and out of potassium and sodium ions becomes disturbed and may even stop. The disturbance of the sodium/potassium transport and ion balance causes an increased osmotic value inside the cells as compared to the cell exterior. The increased relative osmotic value contributes to water passing through the semi-permeable cell membrane and the pressure inside the cell increases. The influx of water causes a swelling of cell diameter and a so called intracellular edema.
United States Patent Application Publication No. 2005/0283091 discloses the usage of bioimpedance for diagnosing and early detection of edema in a tissue. A cross-correlation procedure is employed for obtaining static and dynamic edema indices. The procedure involves generating and applying an excitation signal. A reference signal is also generated to be a normalized, time-delayed version of the excitation signal. A resulting response signal is detected and is cross-correlated to the reference signal by multiplying the two signals and then averaging to obtain a cross-correlation product. The edema indices can then be calculated from the cross-correlation product and the time delay.
A low frequency interval, 10-1000 Hz, is used for estimating the amount of extracellular liquid in a test tissue. A high frequency interval, 10 kHz-10 MHz is also employed for determining the total amount of liquid in a normalized volume of the tissue. The amount of intracellular liquid in the tissue can then be determined as a difference between these two estimated liquid amounts.